The study of the recognition or lack of recognition of cancer cells by a host organism has proceeded in many different directions. Understanding of the field presumes some understanding of both basic immunology and oncology.
Early research on mouse tumors revealed that these displayed molecules which led to rejection of tumor cells when transplanted into syngeneic animals. These molecules are "recognized" by T-cells in the recipient animal, and provoke a cytolytic T-cell response with lysis of the transplanted cells. This evidence was first obtained with tumors induced in vitro by chemical carcinogens, such as methylcholanthrene. The antigens expressed by the tumors and which elicited the T-cell response were found to be different for each tumor. See Prehn, et al., J. Natl. Canc. Inst. 18: 769-778 (1957); Klein et al., Cancer Res. 20: 1561-1572 (1960); Gross, Cancer Res. 3: 326-333 (1943), Basombrio, Cancer Res. 30: 2458-2462 (1970) for general teachings on inducing tumors with chemical carcinogens and differences in cell surface antigens. This class of antigens has come to be known as "tumor specific transplantation antigens" or "TSTAs." Following the observation of the presentation of such antigens when induced by chemical carcinogens, similar results were obtained when tumors were induced in vitro via ultraviolet radiation. See Kripke, J. Natl. Canc. Inst. 53: 333-1336 (1974).
While T-cell mediated immune responses were observed for the types of tumor described supra, spontaneous tumors were thought to be generally non-immunogenic. These were therefore believed not to present antigens which provoked a response to the tumor in the tumor carrying subject. See Hewitt, et al., Brit. J. Cancer 33: 241-259 (1976).
The family of tum.sup.- antigen presenting cell lines are immunogenic variants obtained by mutagenesis of mouse tumor cells or cell lines, as described by Boon et al., J. Exp. Med. 152: 1184-1193 (1980), the disclosure of which is incorporated by reference. To elaborate, tum.sup.- antigens are obtained by mutating tumor cells which do not generate an immune response in syngeneic mice and will form tumors (i.e., "tum.sup.+ " cells). When these tum.sup.+ cells are mutagenized, they are rejected by syngeneic mice, and fail to form tumors (thus "tum.sup.- "). See Boon et al., Proc. Natl. Acad. Sci. USA 74: 272 (1977), the disclosure of which is incorporated by reference. Many tumor types have been shown to exhibit this phenomenon. See, e.g., Frost et al., Cancer Res. 43: 125 (1983).
It appears that tum- variants fail to form progressive tumors because they initiate an immune rejection process. The evidence in favor of this hypothesis includes the ability of "tum.sup.- " variants of tumors, i.e., those which do not normally form tumors, to do so in mice with immune systems suppressed by sublethal irradiation, Van Pel et al., Proc. Natl. Acad. Sci. USA 76: 5282-5285 (1979); and the observation that intraperitoneally injected tum.sup.- cells of mastocytoma P815 multiply exponentially for 12-15 days, and then are eliminated in only a few days in the midst of an influx of lymphocytes and macrophages (Uyttenhove et al., J. Exp. Med. 152: 1175-1183 (1980)). Further evidence includes the observation that mice acquire an immune memory which permits them to resist subsequent challenge to the same tum.sup.- variant, even when immunosuppressive amounts of radiation are administered with the following challenge of cells (Boon et al., Proc. Natl. Acad. Sci. USA 74: 272-275 (1977); Van Pel et al., supra; Uyttenhove et al., supra). Later research found that when spontaneous tumors were subjected to mutagenesis, immunogenic variants were produced which did generate a response. Indeed, these variants were able to elicit an immune protective response against the original tumor. See Van Pel et al., J. Exp. Med. 157: 1992-2001 (1983). Thus, it has been shown that it is possible to elicit presentation of a so-called "tumor rejection antigen" in a tumor which is a target for a syngeneic rejection response. Similar results have been obtained when foreign genes have been transfected into spontaneous tumors. See Fearon et al., Cancer Res. 48: 2975-1980 (1988) in this regard.
A class of antigens has been recognized which are presented on the surface of tumor cells and are recognized by cytolytic T cells, leading to lysis. This class of antigens will be referred to as "tumor rejection antigens" or "TRAs" hereafter. TRAs may or may not elicit antibody responses. The extent to which these antigens have been studied, has been via cytolytic T cell characterization studies, in vitro, i.e., the study of the identification of the antigen by a particular cytolytic T cell ("CTL" hereafter) subset. The subset proliferates upon recognition of the presented tumor rejection antigen, and the cells presenting the tumor rejection antigens are lysed. Characterization studies have identified CTL clones which specifically lyse cells expressing the tumor rejection antigens. Examples of this work may be found in Levy et al., Adv. Cancer Res. 24: 1-59 (1977); Boon et al., J. Exp. Med. 152: 1184-1193 (1980); Brunner et al., J. Immunol. 124: 1627-1634 (1980); Maryanski et al., Eur. J. Immunol. 124: 1627-1634 (1980); Maryanski et al., Eur. J. Immunol. 12: 406-412 (1982); Palladino et al., Cancer. Res. 47: 5074-5079 (1987). This type of analysis is required for other types of antigens recognized by CTLs, including minor histocompatibility antigens, the male specific H-Y antigens, and the class of antigens referred to as "tum-" antigens, and discussed herein.
A tumor exemplary of the subject matter described supra is known as P815. See DePlaen et al., Proc. Natl. Acad. Sci. USA 85: 2274-2278 (1988); Szikora et al., EMBO J 9: 1041-1050 (1990), and Sibille et al., J. Exp. Med. 172: 35-45 (1990), the disclosures of which are incorporated by reference. The P815 tumor is a mastocytoma, induced in a DBA/2 mouse with methylcholanthrene and cultured as both an in vitro tumor and a cell line. The P815 line has generated many tum.sup.- variants following mutagenesis, including variants referred to as P91A (DePlaen, supra), 35B (Szikora, supra), and P198 (Sibille, supra). In contrast to tumor rejection antigens--and this is a key distinction--the tum.sup.- antigens are only present after the tumor cells are mutagenized. Tumor rejection antigens are present on cells of a given tumor without mutagenesis. Hence, with reference to the literature, a cell line can be tum.sup.+, such as the line referred to as "P1," and can be provoked to produce tum.sup.- variants. Since the tum.sup.- phenotype differs from that of the parent cell line, one expects a difference in the DNA of tum.sup.- cell lines as compared to their tum.sup.+ parental lines, and this difference can be exploited to locate the gene of interest in tum.sup.- cells. As a result, it was found that genes of turn variants such as P91A, 35B and P198 differ from their normal alleles by point mutations in the coding regions of the gene. See Szikora and Sibille, supra, and Lurquin et al., Cell 58: 293-303 (1989). This has proved not to be the case with the TRAs of this invention. These papers also demonstrated that peptides derived from the tum.sup.- antigen are presented by H-2.sup.d Class I molecules for recognition by CTLs. P91A is presented by L.sup.d, P35 by D.sup.d and P198 by K.sup.d.
PCT application PCT/US92/04354, filed on May 22, 1992 assigned to the same assignee as the subject application, teaches a family of human tumor rejection antigen precursor coding genes, referred to as the MAGE family. Several of these genes are also discussed in van der Bruggen et al., Science 254: 1643 (1991). It is now clear that the various genes of the MAGE family are expressed in tumor cells, and can serve as markers for the diagnosis of such tumors, as well as for other purposes discussed therein. See also Traversari et al., Immunogenetics 35: 145 (1992); van der Bruggen et al., Science 254: 1643 (1991) and De Plaen, et al., Immunogenetics 40: 360 (1994). The mechanism by which a protein is processed and presented on a cell surface has now been fairly well documented. A cursory review of the development of the field may be found in Barinaga, "Getting Some `Backbone`: How MHC Binds Peptides," Science 257: 880 (1992); also, see Fremont et al., Science 257: 919 (1992); Matsumura et al., Science 257: 927 (1992); Engelhard, Ann. Rev. Immunol. 12:181-207 (1994); Madden, et al, Cell 75:693-708 (1993); Ramensee, et al, Ann. Rev. Immunol. 11:213-244 (1993); Germain, Cell 76: 287-299 (1994). These papers generally point to a requirement that the peptide which binds to an MHC/HLA molecule be nine amino acids long (a "nonapeptide"), and to the importance of the second and ninth residues of the nonapeptide. For H-2K.sup.b, the anchor residues are positions 5 and 8 of an octamer, for H-2D.sup.b, they are positions 5 and 9 of a nonapeptide while the anchor residues for HLA-A1 are positions 3 and 9 of a nonamer. Generally, for HLA molecules, positions 2 and 9 are anchors.
Studies on the MAGE family of genes have now revealed that a particular nonapeptide is in fact presented on the surface of some tumor cells, and that the presentation of the nonapeptide requires that the presenting molecule be HLA-A 1. Complexes of the MAGE-1 tumor rejection antigen (the "TRA" or "nonapeptide") leads to lysis of the cell presenting it by cytolytic T cells ("CTLs").
Research presented in, e.g., U.S. Pat. No. 5,405,940 filed Aug. 31, 1992, found that when comparing homologous regions of various MAGE genes to the region of the MAGE-1 gene coding for the relevant nonapeptide, there is a great deal of homology. Indeed, these observations lead to one of the aspects of the invention disclosed and claimed therein, which is a family of nonapeptides all of which have the same N-terminal and C-terminal amino acids. These nonapeptides were described as being useful for various purposes which includes their use as immunogens, either alone or coupled to carrier peptides. Nonapeptides are of sufficient size to constitute an antigenic epitope, and the antibodies generated thereto were described as being useful for identifying the nonapeptide, either as it exists alone, or as part of a larger polypeptide.
The preceding survey of the relevant literature shows that various peptides, usually eight, nine, or ten amino acids in length, complex with MHC molecules and present targets for recognition by cytolytic T cells. A great deal of study has been carried out on melanoma, and melanoma antigens which are recognized by cytolytic T cells are now divided into three broad categories. The first, which includes many of the antigens discussed, supra, (e.g., MAGE), are expressed in some melanomas, as well as other tumor types, and normal testis and placenta. The antigens are the expression product of normal genes which are usually silent in normal tissues.
A second family of melanoma antigens includes antigens which are derived from mutant forms of normal proteins. Examples of this family are MUM-1 (Coulie, et al, Proc. Natl. Acad. Sci. USA 92:7976-7980 (1995)); CDK4 (Wolfel, et al, Science 269:1281-1284(1995)); Bcatenin (Robbins, et al, J. Exp. Med. 183:1185-1192 (1996)); and HLA-A2 (Brandel, et al, J. Exp. Med. 183:2501-2508 (1996)). A third category, also discussed, supra, includes the differentiation antigens which are expressed by both melanoma and melanocytes. Exemplary are tyrosinase, gp11, gp75, and Melan A/Mart-1. See U.S. Pat. No. 5,620,886 incorporated by reference, with respect to Melan-A. See Wolfel, et al., Eur. J. Immunol. 24: 759 (1994) and Brichard, et al., Eur. J. Immunol. 26: 224 (1996) for tyrosinase; Kang, et al., J. Immunol. 155: 1343 (1995); Cox, et al., Science 264: 716 (1994); Kawakami, et al., J. Imunol. 154: 3961 (1995) for gp 100; Wang, et al., J. Exp. Med. 183: 1131 (1996) for gp 75.
Cytolytic T cells ("CTLs" hereafter) have been identified in peripheral blood lymphocytes and tumor infiltrating lymphocytes of melanoma patients who are HLA-A*0201 positive. See Kawakami, et al, Proc. Natl. Acad. Sci. USA 91:3515 (1994); Coulie, et al, J. Exp. Med. 180:35 (1994). When ten HLA-A*0201 restricted Melan-A specific CTLs derived from different patients were tested, nine of them were found to recognize and react with the peptide Ala Ala Gly Ile Gly Ile Leu Thr Val, (SEQ ID NO: 2), which consists of amino acids 27-35 of Melan-A. (Kawakami, et al, J. Exp. Med. 180:347-352 (1994)). Rivoltini, et al, J. Immunol. 154:2257 (1995), showed that Melan-A specific CTLs could be induced by stimulating PBLs from HLA-A*0201 positive normal donors, and melanoma patients, using SEQ ID NO: 2. The strength of this response has led to SEQ ID NO: 2 being proposed as a target for vaccine development. It has now been found, however, that a decapeptide, i.e., EQU Glu Ala Ala Gly Ile Gly Ile Leu Thr Val (SEQ ID NO: 1),
is actually a better target than SEQ ID NO: 2. This recognition has led to work set forth herein, which is part of the invention.
The majority of peptides which have been identified as binding to HLA-A*0201 are 9 or 10 amino acids in length, and are characterized by two anchor residues. The first is Leu or Met at position 2, and the second is Leu or Val at position 9. See Falk, et al, Nature 351:290 (1991). Ruppert, et al, in Cell 74:929 (1993), show that amino acids found at other positions within a nona- or decapeptide may also have a role in the peptide -HLA-A*0201 interaction. They show, e.g., that a negatively charged residue or proline at position 1 was associated with poor HLA-A*0201 binding.
What is interesting about this work is that the two peptides represented by SEQ ID NOS: 1 and 2 do not possess the major anchor residue at position 2 and, the strong binder SEQ ID NO: 1 has a negatively charged residue at position 1.
A strong binder is not necessarily a stable binder, meaning that the interaction between peptide and HLA molecule may be, and is, brief. When it is desired to induce CTLs, to identify them or to carry out other types of experiments, it would be desirable to have a peptide with the ability to bind to an MHC Class I molecule which binds with high affinity and forms stable complexes. See Van der Burg et al., J. Immunol, 156:3308 (1996).
The invention involves, inter alia, the development of new nonamers and decamers which are surprisingly good HLA binders and CTL stimulators. These molecules, as well as their uses, are among the features of the invention which are set forth in the disclosure which follows.